How do you animate someone holding something with both hands and placing it on the ground?
I don't think you can.  Rather, I would animate them separately. When I've had to open a drawer, I found it best to animate the drawer sliding open first, and then match the character motion.  Drawer's are a little easier, because they follow a straight path.

For this, I would move the box to the ground in a shallow arc, in a reasonable number of frames.  (If it takes 1/2 second, then @ 24fps, you use 14 frames to animate the box.)

Next I would place one or two key frames for Steve.  At least start of move, end of move, and something near the midpoint.  Adjust Steve by tweaking curves or adding keyframes as necessary.